For long path DOAS (Differential Optical Absorption Spectroscopy) technique, it mainly performs qualitative and quantitative analysis about the kind and concentration of trace pollution gas components in the air, based on the absorption features of trace pollution components in the air to the ultraviolet and visible wave band. The technique can monitor a plurality of trace gas components simultaneously with a measurement range from 100 meters to several thousand meters and a high sensitivity.
Generally, as for the application of long path DOAS technique, an emitter installed on a high building is used to generate light ray radiation, then the light ray is collimated and transferred to the atmospheric path through a telescope system; and at the other end (50˜200 meters), a corner reflection mirror is installed for reflecting the light ray back. The light ray reflected through atmospheric path is processed by a spectrometer, then the obtained radiation spectrum is compared with lamp spectrum to get a difference between them to determine the gas components in the atmosphere. Since each kind of gas has its own characteristic absorption spectrum, the kind and concentration of the absorption gas can be determined through the analysis of the variety of spectrum.
However, the following disadvantages do exist when the long optical path gas monitor is used to monitor the gas concentration in the air: the first problem is how to select the locations of the long optical path atmospheric test monitor and installation of the same is also difficult. During the installation, the emitter must be installed at a selected location on a high building, then about 100 meters apart, another location must be selected for the receiver, there being no obstacles between the two selected locations. However, usually after a period of the installation and utilization of the monitor, new obstacles might be generated between the two selected locations, which will bring the problem of re-selection of the two locations.
Next, such remote locations selection is disadvantageous for the maintenance of the long optical path atmospheric test instrument, which needs more work and hours, so the efficiency thereof is low.
In order to overcome the above mentioned drawbacks, the inventor of the present invention, after long period of study and test, finished the present invention.